/*
 * Copyright 2012 Metamarkets Group Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.metamx.metrics;

import com.metamx.common.logger.Logger;

import java.util.HashMap;
import java.util.Map;

public class KeyedDiff
{
  private static final Logger log = new Logger(KeyedDiff.class);

  private final Map<String, Map<String, Long>> prevs = new HashMap<String, Map<String, Long>>();

  public Map<String, Long> to(String key, Map<String, Long> curr)
  {
    final Map<String, Long> prev = prevs.put(key, curr);
    if (prev != null) {
      return subtract(curr, prev);
    }
    else {
      log.debug("No previous data for key[%s]", key);
      return null;
    }
  }

  public static Map<String, Long> subtract(Map<String, Long> xs, Map<String, Long> ys)
  {
    assert xs.keySet().equals(ys.keySet());
    final Map<String, Long> zs = new HashMap<String, Long>();
    for (String k : xs.keySet()) {
      zs.put(k, xs.get(k) - ys.get(k));
    }
    return zs;
  }
}
